1. Field of the Invention
The present invention relates to non-explosive mining techniques for mining operations.
2. Description of the Related Art
Non-explosive mining techniques offer an alternative to the increasing costs associated with explosive excavation. Explosive excavation is a cyclic process requiring several steps: blast holes are drilled into a rock face, explosive charges are loaded into the blast holes, the surrounding area is evacuated, the explosives are detonated, and the area is ventilated and cleared. Explosive excavation incurs significant costs associated with security and environmental damage, such as the generation of toxic gases.
Mechanized non-explosive mining may be carried out with fewer personnel and reduce the security and environmental costs of high explosives. This approach also increases processing efficiency by allowing selective mining of the ore veins. Mechanical impact hammers can be used to excavate hard rock, but the process is slow; the hammers and support equipment are very heavy and the impact tools wear out quickly.
Another example of mechanized non-explosive mining is an impact piston water cannon, in which compressed air drives a heavy piston that impacts and pushes a quantity, or slug, of water. The water slug impacts the rock face to cause erosion and excavation. While impact piston devices have been shown to generate high pressures, their use in commercial excavation work has been limited due to the significant wear on the pistons and cylinders of the devices. Further, the mechanical system that must be maneuvered at the rock face is prohibitively bulky.
As an alternative to an impact piston cannon, a compressed water cannon designed for hard rock mining is described in “A Hydraulic Pulse Generator for Non-Explosive Excavation,” by Kolle, J. J., in Mining Engineering, July 1997, pg. 64-72, which is herein incorporated by reference in its entirety. The compressed water cannon comprises a heavy pressure vessel charged to very high pressures (100-400 MPa, or 14,500-60,000 psi). At these pressures, the water is substantially compressed and stores a considerable amount of energy. After charging, the water is discharged through a fast-opening valve, which causes the resulting pulse of water to impact the rock face. Discharge of a 100 to 400 MPa pulse onto the face of hard rock will have little or no effect in rock fragmentation. To perform rock fragmentation, the compressed water cannon nozzle must be inserted and discharged into a pre-drilled blast hole. Discharge of the pulse into the blast hole generates tensile stresses in the rock and allows effective excavation. The productivity and flexibility of this approach, called bench blasting, is limited because drilling is the most time-consuming aspect of the operation.
As reported by Mauer, W. C. in Advanced Drilling Techniques, pg. 302-348, Petroleum Publishing Inc., 1980, hyper-pressure pulses that are over 1 GPa, or 145,000 psi, have been shown to efficiently excavate hard rock by cratering, eliminating the need for a pre-drilled blast hole. Accordingly, it would be desirable to enable a compressed water cannon to be employed without the need for a pre-drilled blast hole.